Climatic and anthropogenic variations in the sulfide distribution in the Black Sea

Information on the depth of the sulfide onset in the Black Sea has been ana lyzed for the period 1910-1995. Correlation between the depth of the sulfid e onset and the density structure of the layer of the main pycnocline is si gnificant for the entire period covered. Correlation coefficients (R) betwe en the depth of the sulfide onset and the position of isopycnal surfaces in the layer of the main pycnocline vary, on average, 0.71-0.88. The average value of density (sigma(t)) at the depth of sulfide onset, defined as a sul fide concentration equal to 3 mu M, is close to 16.17. Oscillations in the average depth of the sulfide onset range over 24 m and indicate that a stea dy-state trend does not occur. The period of these oscillations may occur o ver a century timescale. The dataset for the period 1960-1995 has been used to analyze temporal variations in concentrations of sulfide inside the ano xic zone of the Black Sea. The results of isopycnal analysis demonstrate th at possible temporal variations in the average position of sulfide onset ve rsus density (sigma(t)) scale do not exceed 0.15, which is close to the lim it of uncertainties for data obtained before 1988. In contrast, a prominent increase in sulfide concentration, as well as nutrient levels, within the anoxic zone is shown and is related to anthropogenic impact.